1. Field of the Invention
The present invention relates in general to the Ethernet Backplane area and, in particular, to an Ethernet switch that has Carrier Class resilience and redundancy characteristics when it interfaces with chassis based application blades (e.g., switches and end stations).
2. Description of Related Art
Ethernet is commonly seen as the most cost efficient networking technology in the Local Area Network (LAN) area. During the past decade, Ethernet has also been increasingly adopted as the technology of choice for other networking applications, such as Wide Area Networks and Public Access Networks. To support these other types of applications, the Ethernet standards framework has been updated and expanded in several ways to achieve the adequate properties and characteristics for each type of usage.
For instance, Ethernet has recently been brought into the local networking domain known as Backplanes, to form the connectivity infrastructure for equipment shelves (a.k.a. subracks) that house computing and switching devices. In view of market demands for a unified manner of using this connectivity infrastructure, the Ethernet standardization forum IEEE 802.3 has embarked on a standards effort in this area, with a task force known as “Ethernet in the Backplane”. The outcome of this effort is expected to be useful for several networking business segments, including the telecommunications sector.
It is notable that this task force is working with a clearly defined scope, which focuses on the physical and electrical aspects of the Backplane. Excluded from the scope are several other aspects that also need to be addressed in order to implement this local connectivity. These aspects include redundancy and resiliency mechanisms which enable one to accomplish “Carrier Class” levels of high availability. It is also notable that the current Ethernet standards framework is associated with building networks that have redundant paths between nodes, but that the fail-over performance of the currently standardized mechanisms fail to accomplish “Carrier Class” levels of high availability.
The present invention is related to the Ethernet Backplane area and has a particular focus on a method for providing Carrier Class resilient (redundant, self-healing) Ethernet connectivity in such an environment. With regard to existing technology and relevant prior art, there are several different types of resiliency solutions some of which are described next.
Standards Compliant Solutions
Traditional resiliency solutions that make use of standard compliant Ethernet LAN devices can be built with a fairly high degree of freedom in terms of network topology even though the Ethernet Standards framework requires a loop-free active topology. This freedom is possible due to the standardized mechanisms for topology discovery and automatic configuration.
These solutions can be built with redundancy on the link and equipment levels, using parallel links and duplicated switches to provide a certain amount of robustness. The parallel links can use IEEE Std 802.3 Link Aggregation, with one or more links manually configured as backup links. When the physical topology includes duplicated switches and redundant crosslinks, IEEE Std 802.1D/Q Spanning Tree Protocols automatically place the relevant links in standby mode to ensure that the active logical topology is loop-free.
In theory, a system based on the above referenced standardized mechanisms could support a deterministic fail-over behavior, but this is not enough. Because, in all of these mechanisms, the time scale for fail-over performance is in the order of seconds, at best. The length of this time scale is such because of the protocols and timers involved in the detection of link failures and the subsequent re-discovery of the active topology. As a result, the time scale for this fail-over performance is 2 to 3 orders of magnitude inferior to that required for Carrier Class performance which is typically 50 ms to 100 ms.
Modified Standards Based Solutions
U.S. Pat. Nos. 6,910,149 and 7,173,934 describe different methods and arrangements for using Ethernet switches with a standards based but modified behavior (i.e. deviating from the standards) to provide resilient connectivity in a LAN. The contents of these patents are incorporated by reference herein.
Both patent applications describe solutions for making a pair of Ethernet switches appear as one resilient Ethernet switch to other devices (switches and end stations) that are attached to the LAN. This is done first by having the pair of Ethernet switches implement a proprietary mechanism that makes the two distinct Ethernet switches appear as one resilient switch. And, then by having each device (switch and end station) use “Link Aggregation” as per IEEE Std 802.3. These methods and arrangements are typically used in general LAN applications.
Even though these solutions and other solutions which are used in currently available Ethernet switching products substantially improve the fail-over characteristics when compared to the standard based solutions, these improvements are in general insufficient: Since these (modified standards based solutions) base their fail-over primarily or solely on failure detection in the physical layer, the fail-over times are largely PHY dependent. This results in a fail-over performance which is around one order of magnitude inferior to that required for Carrier Class performance.
Proprietary Solutions for Specific Use
In the context of Ethernet networking, there are also numerous proprietary solutions for providing redundancy in chassis based nodes, e.g. switches and routers. These solutions are often based on proprietary protocols which are associated with a backplane that is located between a duplicated switch matrix and a duplicated interface board. These protocols and mechanisms which are used on the backplane are strictly internal and hidden from the devices (e.g. switches and end stations) that are connected to the external interfaces of the chassis based node. As such, these solutions are typically designed and optimized for a specific backplane architecture and have strict constraints on internal network topology and size.
Other Solutions for Adjacent Usage Areas
Another though not entirely relevant type of solution is worth mentioning, since its objectives are somewhat similar. This solution is based on a closed loop configuration (Ethernet switching rings), which can be built for example in a LAN or MAN when all of the switches therein implement a particular protocol for topology control. In one implementation of this solution which has been made public in IETF RFC 3619 “Ethernet Automatic Protections Switching” (EAPS), at least one link in the ring is held in hot standby mode, until a node or link failure is detected somewhere in the ring. However, in this type of solution it is common that the traffic disruption time is highly dependent on L1 (PHY) failure detection time. And as described above, fail-over times that are largely PHY dependent result in a fail-over performance that is around one order of magnitude inferior to that required for Carrier Class performance.